OasisLMS

Abstract: Bi-directional load tests on three, large diameter drilled shafts in weakly cemented sandstone at three different sites demonstrate that weakly cemented sandstone can provide significant geotechnical axial resistance in both side and base resistance. Load tests from sites in Minneapolis, Minnesota, Oak Park Heights, Minnesota, and Lansing, Iowa, are presented. The sandstone bedrock at these sites is difficult to sample due to the weak cementation. Despite best efforts of site characterization, estimating representative uniaxial compressive strength for design correlation is difficult due to the low or no sample recovery and poor sample quality. Visual observation of the rock socket drilling, performed with traditional rotary tools for these three projects, also produced spoils that resemble uncemented sand rather than intact sandstone. However, despite the apparent weakness, full-scale load tests demonstrate that the in-situ bedrock is capable of resisting large axial loads in excess of the capacity of the bi-directional jacks for properly constructed drilled shafts. Furthermore, load test results confirm side and base resistance in the weak sandstone bedrock are simultaneously mobilized at small and compatible displacements. This paper presents the subsurface conditions, a summary of the construction, details of bi-directional load test setup, and load test results for each site. The load test results are compared. Recommendations are made for future projects with similar geologic conditions.

Mr. David Graham; Mr. Paul Jason Axtell

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